1. Field of the Invention
The present invention relates to a photoelectric conversion device and an image sensor.
2. Description of the Related Art
As for an example of photoelectric conversion device, there is known a structure as described in, for example, JP 2000-311997 A, which includes a first semiconductor region of a first conductivity type located in a pixel region, a second semiconductor region of a second conductivity type provided in the first semiconductor region for storing a signal charge, a interconnecting portion for connecting the second semiconductor region with a circuit element provided outside the pixel region, and an electrical conductor which is provided above a portion located in the pixel region in the interconnecting portion through an insulating protective film and held at a predetermined potential. In such a structure, a photodiode serving as a light receiving element is formed by a semiconductor PN junction in the pixel region.
Providing the electrical conductor enables, for example, shielding of noise from the outside of the photoelectric conversion device to the interconnecting portion, reducing the electrical influence of the noise on the interconnecting portion. The electrical conductor is made of a metal material such as aluminum, copper, molybdenum, tungsten, or titanium.
Since the electrical conductor is, however, made of the metal material according to the conventional photoelectric conversion device, a pattern made of two metal materials for two layers, one for an interconnecting line of the interconnecting portion and the other for the electrical conductor, is provided in the photoelectric conversion device, making it difficult to reduce a manufacturing steps and resulting cost thereof.
During a process for manufacturing the photoelectric conversion device, for example, a conductive contaminant may be stuck to an upper surface of the interconnecting portion. Presence of a parasitic capacitance caused between the interconnecting portion and the conductive contaminant in parallel to a capacitance of the photodiode increases an effective capacitance of the photodiode, which reduces the sensitivity thereof. The sensitivity is represented by a voltage generated by charges stored in the photodiode and is inversely proportional to the effective capacitance of the photodiode.